<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>后盾人</title>
  </head>
  <body></body>
  <script>
    // "use strict";
    const user = {
      name: "后盾人",
      age: 18
    };
    // Object.preventExtensions(user);
    if (Object.isExtensible(user)) {
      user.site = "houdunren.com";
      console.log(user);
    }
  </script>
</html>
